Generally, a semiconductor package (referred to herein as a “package”) may include a stiffener such as a thin metal ring installed on the top of the package. The stiffener may help prevent warpage of the package. In some cases, a floating (that is, ungrounded) stiffener may become a source of radio frequency interference (RFI) when the stiffener resonates at WiFi band frequencies. A resonating stiffener may behave as an antenna that couples with the signals and further propagates the noise to nearby WiFi radio, which may result in an eventual degradation of radio sensitivity.
In legacy packages, the stiffener may be grounded by one or more Solder Resist Openings (SROs) that may include grounding points to shift the resonant frequencies of the stiffener away from WiFi bands. However, implementation of SROs may complicate design and assembly of the package. Additionally, the SROs grounding scheme may restrict flexibility in trace routing, as the spacing between SROs may need to be less than 8 millimeters (mm) in order to effectively lower the RFI level of the stiffener. Furthermore, the adhesive between the package and the stiffener may need to be made electrically conductive by mixing a conductive material such as silver flakes with non-conductive epoxy, thereby increasing the manufacturing cost of the package. The silver flakes may also decrease bonding strength of the adhesive, and cause delamination of the stiffener over a period of time.